View Full Version : Gas Piston Problem?

July 04, 2007, 18:44
Is the gas piston suppose to freely fall through the gas tube?

Because mine gets stuck with the top of the piston almost lined up with the start of the gas tube. And wont go any more.



July 04, 2007, 19:28
sure you don't have a burr or a bend in the tube. what is the diameter of your piston head?

July 04, 2007, 19:45
What happens if you flip the piston and attempt to put it in backwards? If it stops in the same place, you've narrowed the possible list of problems.

ratas calientes
July 04, 2007, 19:48
Insert the gas piston without the spring. Remove top cover, bolt carrier and bolt. As you tip the rifle forward and back from level, the gas piston should fall freely forward and back. If not, check the gas piston to see if it is bent by rolling it on a flat surface, such as a glass table top. Also check for burrs or dents in gas tube. I have also seen off-center and/or undersize holes in the front of the receiver and/or the gas tube nut (the part that threads into the receiver that holds the read of the gas tube.) http://chilirat.com/emoticons/chilirat.gif

July 04, 2007, 21:39
Does your FAL have the short, soldered in gas tube, or is it the full length version ?

The short versions will cause binding if not aligned properly. Alignment is achieved by applying a bit of force, and usually a plastic mallet at the same time, in the direction the tube has to move. Trial and error.

The long versions can cause problems if the rather delicate ends are bent. This can usually be fixed by removing the retaining pin and gas tube. Flaring the ends out slightly. Then reinstalling the tube and pin. The tube should only be screwed in until it bottoms LIGHTLY, or it'll bend in again, and then backed off slightly to line it up for the retaining pin.

July 04, 2007, 21:44
Right now all I have is a bunch of parts that need to be put together. And this will be my first build, and I do not know much about fALs except from what I can read about them.

I don't have a caliper around right now, but the end of the piston looks like it has some burrs on it.

I also noticed if you look through the gas tube, the diameter changes. The end part of the gas tube (side that connects to the upper receiver) is bigger for 3 1/2 inches, then there is a ridge and the dia. gets smaller for the rest of the way.

So if I put in the gas piston from the other side, it gets caught where the gas tube changes dia.

And if it is put in the right way it gets caught as soon as the piston head meets up with the start of the gas tube.

And the gas piston should move freely through the gas tube.

So I assume the burrs is not letting the gas piston through.

July 04, 2007, 21:48
Ya and if I put the gas piston in backwards, (Piston head first) it gets stuck right away.

So Its probably the burrs on the piston edges. It does not let the piston pass through the smaller dia. part of the gas tube.

July 04, 2007, 21:52
So would it be all right if I just file the burrs off?

July 04, 2007, 22:07
Don't get carried away with the file just yet.
You need to figure out what you have before you start modifying anything.

I take it there is no receiver screwed on to the barrel yet ?

If not, don't worry about whether the gas piston has issues yet.
Things won't and can't really work the way they are supposed to until the barrel is assembled and properly aligned on a receiver. Then worry about the gas tube and THEN worry about the gas piston.

Just curious as to what kind of parts kit you are playing around with ?

Court in Fl
July 04, 2007, 22:44
Punch out the gas tube pin and unscrew the gas tube and then clean the inside of it and check how the piston fits from both ends.

Could be a burr in the tube or on the piston or a little of both.

Check for a burr in the gas block also.

I once had a front sight with a longer threaded section than normal and when it was threaded all the way down it could block the piston.

Court in FL.

July 05, 2007, 09:28
If you already got burrs in the piston, then get an American made one for the parts count. I mean if its that bad.

July 05, 2007, 11:19
Well, I already ordered a new gas piston made by tapco. Along with Falcon Arms HTS kit.

Its a Imbel Parts Kit from Inter Ordnance.

I probly wont do anything now. May be a while before I get a upper receiver. I was just inspecting the parts.

July 06, 2007, 06:59
Welcome Rotor2. What's your location? There might be someone close by that might be able to take a look.

Are you a rotorhead?

July 07, 2007, 17:41
I just checked one of my DSAs. (it's always had an occasional FTE, about once/100 shots...I just haven't gotten around to troubleshooting it with ammo being so expensive)

It has a short gas system, and it turns out that my piston is getting stuck the same way the OP described.

By using a bore light, I found that the narrow portion of the tube was all rusty, so I scrubbed it with a .45 cal bore mop and some valve grinding compound.....drops freely through either way now.

I may just have to break into my stash of ammo tomorrow and try her out now:D

July 08, 2007, 20:46
I just bought a USA made Tapco gas piston and it slides just fine through the gas tube.

I'm pretty sure it was just the burrs on the piston.

Anyways I'm way up in MN.

And yes I'm a rotorhead.

July 08, 2007, 21:48
Those half US century pistons with the us shaft screwed onto a foriegn piston top warp at the part where it screws in. This might cause folks problems.

July 09, 2007, 19:21
It sounds like an engineering problem from the beginning.

July 11, 2007, 04:05

You should do as Court in Fl said. Unscrew the Gas adjuster nut and punch out the roll pin, then unscrew the tube. The tube may have been screwed in to much at some point and compressed the thread end where the piston head enters the tube. [or just check for burrs at the end threads].

One more point! If the threads were causing this and your new Tapco Piston fits before the fix, the Tapco Piston my be too small of a diameter at the head. Thus possibly releasing too much gas and with it possibly causing a future cycling problem.


July 11, 2007, 09:26
He doesn't have a receiver screwed on to that barrel yet guys.
He MAY still have a stub on the barrel. He hasn't said.
Regardless, it's a bit early in the game to get all worked up over whether the gas piston is binding since nothing permanent is lined up yet.

July 11, 2007, 21:47
Right now the gas tube is separate from everything else. I already detached it from the barrel. Barrel is off the stub. Everything is ready to be put on the upper receiver when I get one.

So we will just have to wait till It starts going together.

July 12, 2007, 01:17
...we'll be here when it does.